The Influence of Road Verges on the Use of Nearby Small Shrubland Remnants by Birds in the Central Wheatbelt of Western Australia

Abstract

In the Kellerberrin District of the Western Australian wheatbelt, about 60% of the remnants of native vegetation are smaller than 10 ha. We studied the variation in bird abundance in 13 small remnants (range 0·03–6·71 ha) of shrubland isolated in farmland by distances of 70–600 m from the nearest native vegetation, a road verge. Overall, 31 species were recorded in the remnants and nearby road verges, and species richness varied from 7 to 15 at individual sites. Regression analysis showed that the structural attributes of verges and the number of birds found in verges were more often significant predictors of variation in the number of individuals of the most common 19 species censused in remnants than were the structural attributes in the remnants themselves. The diversity of all bird species and the richness of species dependent on native vegetation decreased significantly with the distance of remnants from road verges. For a group of 10 species of small passerines, species richness, species turnover, and variation in the number of individuals between consecutive censuses all were negatively related to the distance between remnants and road verges. For five of these 10 species, there were fewer individuals in remnants than in adjacent road verges when the distance between them exceeded 110 m. However, for less-isolated remnants (≤110 m), only one species showed a significant difference in abundance. It is concluded that these small shrubland remnants are primarily used by birds moving to and from adjacent areas of native vegetation, in this case road verges. The value of small remnants of vegetation as parts of the conservation network decreases with their isolation, and is strongly linked to the use of road verges by the shrubland bird community.